You want to install them with the slit in the hinge perpendicular to the trailing edge of the wing/stabilizer. Slide the hinge in so tha the slit is sticking out. The slits are there to help the CA to wick into the back of the hinge.

For more help on installing CA hinges check out Minnflyer's How-to on CA Hinges:

[link=http://www.rcuniverse.com/magazine/article_display.cfm?article_id=55]Installing CA Hinges[/link]

Hope this helps

Ken